The present invention generally relates to a color electronic photographic apparatus which can be applied to a color duplicating machine, a color printer and so on.
In order to form color images with an electronic photograph, a method of superposing the toner images of the respective colors of yellow, magenta, cyanide, and black on a transfer material so as to form color images is provided. As methods of effecting the superposition of the toner images on the transfer material, there have been provided a transfer drum system for rotating a transfer material around the transfer drum so as to repeatedly bring it to the same image forming position, where the sequentially formed toner images of each color are transferred in piles, and a continuous superposing system for arranging a plurality of image forming portions side by side so as to let the transfer material be carried by belts or the like to pass by the positions of the respective image forming portions so that the toner images of each color are transferred sequentially and are superposed.
There is an example of a color image forming apparatus shown in Japanese Laid-Open Patent Application No. 1-252982, which uses the transfer drum system discussed above.
FIG. 7 shows the overall construction of the conventional embodiment, which will be described hereinafter with respect to its construction and operation. In FIG. 7, reference numeral 101 is a photosensitive material. A charger 102, a developer portion 103, a transfer drum 104, and a cleaner 105 are positioned opposite the photosensitive material 101. The developer portion 103 is composed of a Y developer 106 for making the toner image of a yellow color, an M developer 107 for making a magenta color, a C developer 108 for making a cyanide color, and a K developer 109 for a black color. The respective developers are positioned in sequence opposite the photosensitive material 101 so that the developing operation can be effected through rotation of the whole developer mechanism 103.
The transfer drum 104 and the photosensitive material 101 are rotated at a constant speed in the directions respectively indicated by arrows in FIG. 7 while being positioned opposite one another during the operation.
When the operation starts, the photosensitive material 101 is rotated in the arrow direction, and the surfaces are charged evenly by the charger 102.
A laser beam 110 modulated by a signal for forming the yellow image of a first color impinges upon the surfaces of the photosensitive material so as to form latent images. The latent images are developed first by the Y developer 106 opposite to the photosensitive material so as to form a yellow toner image. One sheet of paper such as a transfer material fed from the paper feeding portion 111 is caught at its tip end by a pawl portion 112 and is already wound on the outer periphery of the transfer drum 104 by the time the yellow toner image reaches a position opposite the transfer drum 104. The timing is set so that the yellow toner image on the photosensitive material may reach a position opposite the given position of the paper so as to form the toner images.
The yellow toner image on the photosensitive material is transferred onto the paper by the function of the transfer charger 113, and thereafter, the photosensitive material surfaces are cleaned by the cleaner 105 so as to prepare for image formation with the next color. The toner images of magenta, cyanide, and black are then sequentially and continuously formed in a similar manner. At this time, each developer of the developer portion 103 is positioned opposite the photosensitive material when it is desired to develop the corresponding color. The diameter of the transfer drum is sufficient for the longest paper to be wound thereabout, and the developer portion 103 may be moved to develop the images of the respective colors.
The illumination by the laser beam 110 for forming images of the various colors is timed so that the toner image of each color and the toner images already transferred onto the paper on the transfer drum may be positioned in conformity. In this manner, four colors of toner images are transferred in a superposed manner onto the paper on the transfer drum 104 so that the color images are formed on the paper. After the toner images of all the colors have been transferred, the paper is peeled off from the transfer drum 104 with the peeling pawl 114. The upper toner images are fixed by a fixer 116 as the paper is carried through the carrying portion 115 to discharge the paper out of the apparatus. The above description is a brief description of the construction and the operation of a conventional embodiment.
Japanese Laid-Open Patent Application No. 1-250970 is among examples of color image forming apparatus using a continuous transferring system. Four colors of image forming stations each including a photosensitive material, a light scanning means and so on are arranged side by side to form four-color images in the example. Paper carried by the belt passes under the lower portion of the respective photosensitive material so as to superpose the toner images.
A method of reciprocating the transfer material with respect to the photosensitive material so as to repeat the transferring operation and superpose the toner images is disclosed in U.S. Pat. No. 4,905,048 as another method for superposing toner images of different colors on the transfer material so as to form color images.
In the transfer drum system of such conventional embodiments as described hereinabove, a transfer drum is used so as to position the toner images of different colors to provide proper superposition. The transfer drum is rotated at the same speed as the photosensitive material, and further the timing of the movement of the tip end of the image is set so that the mutual positions of the toner images of the different colors are put into conformity. As the paper is required to be wound around the transfer drum in the construction described hereinabove, the diameter of the constant-size transfer drum must be large and the construction is very complicated so that the apparatus is quite large.
It has been impossible to use stiff paper such as postcards, thick paper or the like because it could not be wound around the transfer drum.
The continuous transfer system has a number of image forming positions corresponding to the number of colors. No transfer drum is necessary as the paper has only to pass there one after another. But in this case, the latent image forming means of the laser optical system and so on for forming latent images on the photosensitive material are necessary in accordance with the number of the colors, thus resulting in a very complicated construction in this portion. As the image forming positions are plural in number, the relative positional relation of the image forming portions of the respective colors has a large influence upon the color divergence.
It is especially important to provide correct positional alignment among the respective colors of the latent images by the latent image forming means. This requires a complicated construction of the image light exposing system as the latent image forming means as shown by way of example in Japanese Laid-Open Patent Application No. 1-250970.
In the example disclosed in the U.S. Pat. No. 4,905,048 for reciprocating the transfer material, the photosensitive material becomes large as the toner images of the various colors are formed in order on one photosensitive material, and the construction and control for combining the sensitive body with the developer for each color is very complicated such that the maintenance required to exchange them is difficult.